1. Field of the Invention
The present invention relates to an oxide based superconducting material capable of exhibiting a superconductive property when cooled with liquid helium or liquid nitrogen, a superconductor capable of transmitting a superconducting current under cooled condition with liquid helium or liquid nitrogen, a process for the production thereof, and a superconducting wire, superconducting coil, and magnetic shield substance comprising the superconducting material.
2. Description of Related Art
Conventional high temperature oxide based superconducting containing Tl, Sr, Ca, Cu, and O as major elements have a superconducting critical temperature as high as about 120 K. as reported in Physica C vol. 183, pp. 67-72; Proceedings, Vol. 235, Materials Research Society Symposium, Boston, Dec. 1st-6th, 1991; Japanese Patent KOKAI (Laid-open) No. Hei 4-300202; and Japanese Patent KOKAI (Laid-open) No. Hei 5-816. Although they are very promising materials which could have succeeded in the introduction of pinning centers thereinto, i.e., the prerequisite for achieving a high critical current density, they are difficult to retain such a high critical current density as transmission current when formed into superconducting wires as well as to make into practical products, through which an actual superconducting current can be passed.
Satisfactory consideration has not been given heretofore to the electrical connections between the crystal particles of superconducting material present in the conventional superconducting wires, i.e., the connections of grain boundaries, across which a sufficient superconducting current can be passed. Therefore, there has been a problem that the critical current density is drastically reduced only by applying a slight magnetic field to the superconducting materials.